In recent years, multifunctional and high-performance semiconductor devices are continuously proposed. In response to the proposals, materials other than silicon (Si) are newly adopted to the substrate of the semiconductor device. Among those substrate materials, sapphire, SiC (for power device), and GaN (for light-emitting diode (LED)) etc. draw special attention to meet the proposals. On the other hands, it is desired to develop new processing methods of substrate, in order to achieve a mass-production of more high-performance devices at low cost.
In a manufacturing process of the semiconductor device, a polishing process is performed to flat the surface of the semiconductor substrate. In a conventional polishing process, oil slurry including diamond abrasive particles is used. Specifically, the surface of the semiconductor substrate formed from silicon carbide is mechanically polished by the diamond abrasive particles harder than silicon carbide. Since the polishing rate of this process is high, the polishing amount reaches a target amount in a short period of time. However, there is a risk of greatly damaging the surface of the substrate. In short, it is difficult to obtain a high quality of polishing surface. Furthermore, since the quality of the oil slurry is changed by the heat generated during the polishing process, the diamond abrasive particles contained in the slurry aggregate. As the result, the expensive diamond particles cannot be reused.
To solve the above problem, a polishing method utilizing a mechanochemical effect has been introduced (Patent Document 1). In the mechanochemical polishing, the surface of the object material is altered, and then polished by abrasive particles softer than the object material. Thus, the surface of the object material is not damaged so much. Further, in order to improve the polishing rate, techniques polishing silicon carbide with oxidizing agent are introduced (Patent Documents 2, 3 and 4).